The objective of this project is to study the mechanism(s) of chemically induced leukemia. Two major aspects are focused on: (l) characterizing the covalent interactions of chemical carcinogens with cellular DNA in hemopoietic tissues both in vivo and in vitro, and (2) examining the effects of these covalent interactions of chemical carcinogens and cellular DNA on the proliferation and differentiation of hemopoietic target cells. Leukemogenic chemicals which are under investigation include 7,l2-dimethylbenz[a]anthracene (DMBA), N-methylnitrosourea (MNU), derivatives of 2-acetylaminophenanthrene (AAP), representing the polycyclic hydrocarbons, direct alkylating agents, and aromatic amines, respectively. Results obtained so far are (1) detection of N-(guanin-8-yl)-2-aminofluorene (Gua-C8-AAF) in bone marrow and spleen cells of Fischer 344 rats following an intravenous dose of N-hydroxy-acetylaminofluorene (N-OH-AAF) or N-acetoxy-2-acetylaminophenanthrene (N-OAc-AAP), (2) development of a murine multipotential hemopoietic stem cell colony assay which consists of pure and mixed colonies (granulocyte, erythrocyte, megakaryocyte, macrophage and mast cells). Future studies will include (1) determination of in vivo formation of DNA adducts with N-OH-AAP and N-OAc-AAP which are more leukemogenic than the acetylaminofluorenes, (2) development of a murine hemopoietic blast cell colony assay which contains only undifferentiated cells, and (3) investigation of the biological interactions of DMBA, MNU, N-acetylaminofluorene (N-OAc-AAF), and N-OAc-AAP on hemopoietic target cells using these stem cell assays.